The fine comes only two days after American Airlines' parent company, AMR Corp., emerged from bankruptcy and joined with US Airways to form the world's largest carrier.

The federal agency said the airline's reservation agents, on a number of occasions in 2012 and 2013, described airline surcharges as government taxes, in violation of federal full-fare advertising rules.

In addition, pop-ups on the airline’s website claimed that the surcharges were taxes.

In a letter to the Department of Transportation, American Airline attorneys called the violations "inadvertent mistakes" and were "clearly not the intention of American to attempt to deceive its customers into thinking that surcharges imposed by American or by other carriers are actually government taxes."

The airline said it has given its reservation agents further training and corrected its website to avoid further violations.

Under the department's full-fare advertising rule, airlines must quote the entire price of an airline ticket, including all taxes, fees and surcharges. If asked to break out the components of the fare, they must explain what is a government tax and what is a service fee or surcharge added by the carrier.

Last month, the Department of Transportation issued a $20,000 fine against American Airlines over a "kids fly free" promotion that was not free of taxes and fees.